The complete mitochondrial genome of Melanostoma mellinum (Linnaeus, 1758) (Diptera: Syrphidae) and phylogenetic analysis

Abstract In this study, the complete mitochondrial genome (mitogenome) of Melanostoma mellinum (Linnaeus, 1758) was sequenced using the-next generation sequencing technology. The assembled mitogenome of M. mellinum has a total length of 16,055bp and contains 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), and 2 ribosomal RNA genes (rRNAs). The results of phylogenetic reconstruction based on the combined mitochondrial gene dataset indicated that M. mellinum belongs to Melanostoma genus with a close relationship to Melanostoma orientale, but the monophyly of the tribe Bacchini is not well supported.

Syrphidae (Insecta, Diptera) comprise almost 6200 described species worldwide (Evenhuis and Pape 2021) and are wellknown by nature enthusiasts and researchers because they provide several crucial ecosystem services (Dunn et al. 2020), such as pollination, biological control of pests and organic matter recycling (Inouye et al. 2015;Moerkens et al. 2021). Among the subfamily Syrphinae, Melanostoma mellinum (Linnaeus, 1758) is a small hoverfly with yellow and black markings, which can be well distinguished from other Melanostoma species by the following morphological features: face, scutellum, and mesonotum shining black; male adults have nearly square yellow markings on abdominal segments 3 and 4; female adults have inverted yellow triangle markings on abdominal segments 3 and 4 (Huo et al. 2007). The systematic status of the genus Melanostoma is still controversial, as this genus has been placed into the subfamily Melanostominae (Williston 1885), tribe Melanostomini (Hull and Riley 1949;Vockeroth 1969Vockeroth , 1990, or classified into the tribe Stenosyrphini (Goffe 1952), or Bacchini (Rotheray and Gilbert 1989). The monophyletic status of the tribe Bacchini is also challenged by the molecular phylogenetic works (Thompson and Skevington 2014;Ståhls et al. 2003). In this study, we obtained the complete mitogenome data of M. mellinum and build the phylogenetic tree to reconstruct its evolutionary relationships.
The specimen of M. mellinum was collected from the Changqing National Nature Reserve (107 17'E, 33 19 0 N) in 2019, and stored in the Museum of Zoology and Botany, Shaanxi University of Technology, Hanzhong, China (SUHC) (Accession number: R81, https://www.snut.edu.cn/, Le Zhao, email: Lezhao@snut.edu.cn). The genomic DNA of M. mellinum was extracted using the DNeasy kit (Qiagen, Hilden, Germany), then paired-end libraries (2 Â 150 bp) with 400 bp insert sizes were constructed and sequenced by an lllumina HiSeq 4000 platform. We used the software MITOZ (Meng et al., 2019) to assemble and annotate the complete mitogenome, with the putative control region being delineated by tRNA boundaries.
The complete mitogenome of M. mellinum was 16,055 bp in length, including 37 typical mitochondrial genes (13 PCGs, 22 tRNAs, 2 rRNAs) and a putative AT-rich control region (D-loop), which has been deposited in GenBank (accession number: OK032510). The base composition of M. mellinum mitogenome was 41.2% A, 40% T, 10.6% C, and 8.2% G, with a positive AT-skew (0.014) and a negative GC-skew (À0.123), and all genes were arranged in the same order like other syrphids (Le and Gang, 2020;Zhou et al. 2021). Eight overlaps and 8 intergenic spacers were found in the mitogenome of M. mellinum, with the longest intergenic spacer of 23 bp located between trnL1 and rrnL. All 13 PCGs used ATN as the start codon (cox1, atp6, and nad1 used ATA, nad2, nad3, nad5 and nad6 used ATT, cox2, cox3, nad4, nad4L, and cytb used ATG, atp8 used ATC), a total of 12 PCGs used TAA as the stop codon except ND3, which stopped with TAG.
To check the phylogenetic status of M. mellinum, we reconstructed a phylogenetic tree using all available mitogenome sequences of subfamily Syrphinae species in the NCBI database, and two Eristalinae species were used as an outgroup. Sequence alignments of 13 PCGs were generated by software MAFFT v7.313 with the E-INS-I strategy (Katoh and Standley 2013), and the best fit model of the partition scheme was determined by program PartitionFinder2 v2.1.1 with AICc scoring criteria (Lanfear et al. 2017). Phylogenetic trees were inferred with Bayesian inference (BI) and maximum likelihood (ML) by CONTACT (Ronquist et al. 2012) and IQ-tree v1.6.8 (Nguyen et al. 2015), respectively. The tree topologies reconstructed by ML and BI methods were consistent ( Figure 1) and supported the close relationships of M. mellinum with M. orientale within Melanostoma genus, but the monophyly of tribe Bacchini is not supported.

Ethical approval
Ethics approval was not required for this study. All procedures performed in this study involving animals followed the Guidelines for Shaanxi University of Technology, Hanzhong, China. The field studies did not involve vertebrates, regulated invertebrates, endangered or protected species.

Author contribution
Le Zhao, Keke Huo and Gang Li conceived and designed the experiments; Yicheng He performed the experiments; Le Zhao and Hanyue Liu analyzed the data; Le Zhao and Hanyue Liu wrote the paper.

Disclosure statement
No potential conflict of interest was reported by the author(s). Figure 1. The Bayesian Inference (BI) and Maximum-Likelihood (ML) phylogenetic tree of Subfamily Syrphinae species based on the 13 PCGs. Statistical support values (Bootstrap/posterior probability) of ML/BI methods are shown below each node.